Transactions are here…

MongoDB 4.0 adds support for multi-document ACID transactions, making it the only open source database to combine the speed, flexibility, and power of the document model with ACID guarantees. Through snapshot isolation, transactions provide a consistent view of data, and enforce all-or-nothing execution to maintain data integrity.

ACID transactions are a key capability for business critical transactional systems, specifically around commerce processing. No other database has both the power of NoSQL and cross collection ACID transaction support. This combination will make it easy for developers to write mission critical applications leveraging the power of MongoDB"

Safe secondary reads: providing consistent reads against secondary replica set members, even while data is being rebalanced across a cluster. Hear from Dianna Hohensee, MongoDB software server engineer.